1. Technical Field
The present disclosure relates generally to devices that may be used in tissue ablation procedures. More particularly, the present disclosure relates to devices and methods for maintaining ablation temperatures surrounding microwave antennas radiofrequency probes during ablation procedures.
2. Background of Related Art
In the treatment of diseases such as cancer, certain types of cancer cells have been found to denature at elevated temperatures which are slightly lower than temperatures normally injurious to healthy cells. These types of treatments, known generally as hyperthermia therapy, typically utilize electromagnetic radiation to heat diseased cells to temperatures above 41° Celsius while maintaining adjacent healthy cells at lower temperatures where irreversible cell destruction will not occur. Other procedures utilizing electromagnetic radiation to heat tissue also include ablation and coagulation of the tissue. Such ablation procedures, e.g., such as those performed for menorrhagia, are typically done to ablate and coagulate the targeted tissue to denature or kill the tissue. Many procedures and types of devices utilizing electromagnetic radiation therapy are known in the art. Such therapy is typically used in the treatment of tissue and organs such as the prostate, heart, kidney, lung, brain, and liver.
Presently, there are several types of microwave probes in use, e.g., monopole, dipole, and helical, which may be inserted into a patient for the treatment of tumors by heating the tissue for a period of time sufficient to cause cell death and necrosis in the tissue region of interest. Such microwave probes may be advanced into the patient, e.g., laparoscopically or percutaneously, and into or adjacent to the tumor to be treated. The probe is sometimes surrounded by a dielectric sleeve.
However, in transmitting the microwave energy into the tissue, the outer surface of the microwave antenna typically may heat up and unnecessarily desiccate, or even necrose, healthy tissue immediately adjacent the antenna outer surface. This creates a water or tissue phase transition (steam) that allows the creation of a significant additional heat transfer mechanism as the steam escapes from the local/active heating area and re-condenses further from the antenna. The condensation back to water deposits significant energy further from the antenna/active treatment site. This local tissue desiccation occurs rapidly resulting in an antenna impedance mismatch, which both limits power delivery to the antenna and effectively eliminates steam production/phase transition as a heat transfer mechanism for tissue ablation.
To prevent the charring of adjacent tissue, several different cooling methodologies are conventionally employed. For instance, some microwave antennas utilize balloons which are inflatable around selective portions of the antenna to cool the surrounding tissue. Thus, the complications associated with tissue damaged by the application of microwave radiation to the region are minimized. Typically, the cooling system and the tissue are maintained in contact to ensure adequate cooling of the tissue.
Other devices attempt to limit the heating of tissue adjacent the antenna by selectively blocking the propagation of the microwave field generated by the antenna. These cooling systems also protect surrounding healthy tissues by selectively absorbing microwave radiation and minimizing thermal damage to the tissue by absorbing heat energy.